Abnormality diagnosis apparatus of internal combustion engine

ABSTRACT

An abnormality diagnosis apparatus of an internal combustion engine is provided which is capable of improving reliability in abnormality determination as well as making abnormality determination at high frequencies. The abnormality diagnosis apparatus includes an oxygen sensor for detecting a concentration of oxygen in exhaust gases of an internal combustion engine, an injector for injecting fuel into the internal combustion engine, a feedback control element for driving the injector according to the concentration of oxygen to control an amount of fuel supplied to the internal combustion engine in a feedback manner, a forced fuel correction element for correcting an amount of fuel controlled by the feedback control element in a forced manner, and an abnormality determination element for determining the presence or absence of abnormality in the injector. The abnormality determination element determines the presence or absence of abnormality in the injector based on the concentration of oxygen detected by the oxygen sensor in the course of a forced fuel correction control operation carried out by the forced fuel correction element.

[0001] This application is based on Application No. 2001-328890, filedin Japan on Oct. 26, 2001, the contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an abnormality diagnosisapparatus of an internal combustion engine for determining abnormalityin a fuel system (e.g., injector(s)) used in a vehicle engine and so on,and more particularly, to such an abnormality diagnosis apparatus of aninternal combustion engine which is capable of improving reliability inthe abnormality determination as well as making abnormalitydetermination at high frequencies.

[0004] 2. Description of the Prior Art

[0005] In general, in a control system for an internal combustionengine, in order to perform feedback control on the amount of fuelinjected from each injector in accordance with the operating conditionof the engine, an oxygen sensor is provided on an exhaust pipe fordetecting the concentration of oxygen in exhaust gases flowingtherethrough so that the amount of fuel to be injected from eachinjector can be controlled in a feedback manner in accordance with theoxygen concentration thus detected.

[0006] In addition, during the operation of the internal combustionengine, it is necessary to diagnose the functionality of the fuel systemincluding the injectors or the oxygen sensor so as to maintain thefeedback control on the amount of fuel supplied to the internalcombustion engine in a reliable manner.

[0007] In these circumstances, there have been conventionally proposed avariety of abnormality diagnosis apparatuses for determining thepresence or absence of abnormality in a fuel system or an oxygen sensorin an internal combustion engine.

[0008] For instance, as a first prior art example, Japanese PatentApplication Laid-Open No. 4-269350 or Japanese Patent ApplicationLaid-Open No. 6-17692 describes an apparatus for determining abnormalityin a fuel system for a part of engine cylinders based on the state of anoutput signal from an oxygen sensor.

[0009] However, since in the above-mentioned first prior art example,the feedback condition based on the detection signal of the oxygensensor is not specified, there would be a fear that when the detectionsignal of the oxygen sensor is varied by external disturbances (changesin load or in the number of revolutions per minute of the engine, etc.)other than abnormality in the fuel system, it might be determined bymistake that there has taken place abnormality.

[0010] Moreover, as a second prior art example, Japanese PatentApplication Laid-Open No. 2-11840 describes an apparatus for determiningabnormality in an oxygen sensor based on the state of a signal from theoxygen sensor representative of the concentration of oxygen detected inthe course of a forced fuel correction control operation.

[0011] However, in this second prior art example, abnormalitydetermination for the oxygen sensor is made only during the forced fuelcorrection control operation, and hence it is impossible to carry outoxygen sensor abnormality determination with high frequencies or highlyfrequently.

[0012] Additionally, as a third prior art example, Japanese PatentApplication Laid-Open No. 63-219848 describes an apparatus fordetermining abnormality in a fuel system by using the amount of fuelcontrolled in a feedback manner based on a detection signal (oxygenconcentration) of an oxygen sensor and the amount of control learned forthe feedback-controlled fuel amount.

[0013] However, in the third prior art example, it is only possible todetect abnormality in the entire fuel system, but not to detectabnormality in a part of the fuel system for respective enginecylinders.

[0014] As described above, the prior art abnormality diagnosisapparatuses have the following problems. That is, in the first prior artexample, when the detection signal of the oxygen sensor is disordered byexternal disturbances other than abnormality in the fuel system, itmight mistakenly be determined that the oxygen sensor is abnormal.

[0015] In addition, in the second prior art example, it is impossible todetect abnormality in the oxygen sensor with high frequencies or highlyfrequently.

[0016] Moreover, in the third prior art example, it is impossible todetect abnormality in the fuel system for a part of cylinders.

SUMMARY OF THE INVENTION

[0017] The present invention is intended to obviate the various problemsas referred to above, and has for its object to provide an abnormalitydiagnosis apparatus of an internal combustion engine which is capable ofimproving reliability in abnormality determination as well as makingabnormality determination at high frequencies or highly frequently.

[0018] Bearing the above object in mind, according to the presentinvention, there is provided an abnormality diagnosis apparatus of aninternal combustion engine including: an oxygen sensor for detecting aconcentration of oxygen in exhaust gases of an internal combustionengine; an injector for injecting fuel into the internal combustionengine; a feedback control element for driving the injector according tothe concentration of oxygen to control an amount of fuel supplied to theinternal combustion engine in a feedback manner; a forced fuelcorrection element for correcting an amount of fuel controlled by thefeedback control element in a forced manner; and an abnormalitydetermination element for determining the presence or absence ofabnormality in the injector. The abnormality determination elementdetermines the presence or absence of abnormality in the injector basedon the concentration of oxygen detected by the oxygen sensor in thecourse of a forced fuel correction control operation carried out by theforced fuel correction element.

[0019] In a preferred form of the present invention, the forced fuelcorrection element carries out the forced fuel correction control on theamount of control fuel when the operating condition of the internalcombustion engine is in a stable state.

[0020] In another preferred form of the present invention, beforedetermining the presence or absence of abnormality in the injector, theabnormality determination element determines the presence or absence ofabnormality in the oxygen sensor based on the concentration of oxygendetected by the oxygen sensor in the course of the forced fuelcorrection control operation carried out by the forced fuel correctionelement, and further determines the presence or absence of abnormalityin the injector only when the oxygen sensor is not abnormal.

[0021] In a further preferred form of the present invention, theabnormality determination element is provided with warning informationelement and drives the warning information element when it is determinedthat the oxygen sensor or the injector is abnormal.

[0022] In a still further preferred embodiment of the present invention,when the amount of fuel controlled by the feedback control elementvaries from a reference value by a prescribed value or more, theabnormality determination element determines that the amount of controlfuel is abnormal, and further determines that the fuel system includingthe injector is abnormal when it is determined that at least one of theinjector and the amount of control fuel is abnormal.

[0023] The above and other objects, features and advantages of thepresent invention will become more readily apparent to those skilled inthe art from the following detailed description of preferred embodimentsof the present invention taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a block diagram illustrating the construction of anabnormality diagnosis apparatus of an internal combustion engineaccording to a first embodiment of the present invention.

[0025]FIG. 2 is a flow chart illustrating a processing operation of theabnormality diagnosis apparatus according to the first embodiment of thepresent invention.

[0026]FIG. 3 is a flow chart illustrating another processing operationof the abnormality diagnosis apparatus according to the first embodimentof the present invention.

[0027]FIG. 4 is a flow chart illustrating the processing operation of anabnormality diagnosis apparatus of an internal combustion engineaccording to a second embodiment of the present invention.

[0028]FIG. 5 is a flow chart illustrating the processing operation of anabnormality diagnosis apparatus of an internal combustion engineaccording to a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, preferred embodiments of the present invention willbe described in detail while referring to the accompanying drawings.

[0030] Embodiment 1.

[0031]FIG. 1 is a block diagram in which a first embodiment of thepresent invention is shown.

[0032] In FIG. 1, an intake pipe 2 and an exhaust pipe 3 are connectedwith an internal combustion engine 1 (hereinafter simply referred to asan engine).

[0033] A throttle valve 4 is arranged in the intake pipe 2 for adjustingthe amount of intake air supplied to the engine 1.

[0034] In addition, injectors 5 each supplying fuel to a correspondingset of cylinders are provided at an air introduction portion or intakemanifold through which air is introduced from the intake pipe 2 into theengine 1. Here, note that only one injector 5 is shown to avoid thecomplexity in the drawings.

[0035] Moreover, an air flow sensor 6 for detecting the amount of intakeair is provided on the intake pipe 2 on the upstream side of thethrottle valve 4, and a throtle opening sensor 7 for detecting thedegree of opening of the throttle valve 4 (hereinafter referred to asthrottle opening) is mounted on the throttle valve 4.

[0036] The air flow sensor 6 outputs a number of pulses corresponding tothe amount of intake air introduced into the engine 1.

[0037] In addition, a crank angle sensor 8 for detecting a referencerotational position of the engine 1 (i.e., a prescribed rotational angleor position of a crankshaft) is mounted on an rotation shaft (i.e.,crankshaft) of the engine 1, and an oxygen sensor 9 for detecting theconcentration of oxygen (corresponding to an air fuel ratio) in exhaustgases is provided in the exhaust pipe 3.

[0038] The crank angle sensor 8 outputs the number of pulsescorresponding to the number of revolutions per minute of the engine 1.

[0039] The air flow sensor 6, the throttle opening sensor 7, the crankangle sensor 8 and the oxygen sensor 9 together constitute a variety ofkinds of sensors for detecting the operating condition of the engine 1.Other sensors not illustrated in the drawings include a pressure sensorfor detecting the internal pressure in the intake pipe 2, a temperaturesensor for detecting the temperature of engine coolant or cooling waterfor cooling the engine 1, and so on.

[0040] The detection signals of the various sensors are input to anelectronic control unit 10 at prescribed crank angles, respectively.

[0041] The electronic control unit 10 is provided with an inputinterface circuit 11 for receiving the detection signals from thevarious sensors 6-9, a microcomputer 12 for processing a variety ofkinds of input information, and an output interface circuit 13 foroutputting various control signals based on the operational processingof the microcomputer 12.

[0042] The microcomputer 12 is provided with a feedback control element121 for controlling the amounts of fuel to be injected from theinjectors 5 to the unillustrated intake manifold in a feedback manner, aforced fuel correction element 122 for forcedly correcting the amountsof fuel to be injected from the injectors 5, and an abnormalitydetermination element 123 for determining the presence or absence ofabnormality at least in the injectors 5.

[0043] The feedback control element 121 controls the amount of fuelsupplied to the engine 1 in a feedback manner by controlling the drivingtime of each injector 5 in accordance with the concentration of oxygendetected by the oxygen sensor 9.

[0044] When it is determined that there is abnormality in any of theinjectors 5, the forced fuel correction element 122 forcedly correctsthe amounts of control fuel which are injected from the injectors 5 andcontrolled by the feedback control element 121.

[0045] The abnormality determination element 123 determines the presenceor absence of abnormality in the injectors 5 based on the concentrationof oxygen detected by the oxygen sensor 9 in the course of a forced fuelcorrection control operation performed by the forced fuel correctionelement 122.

[0046] A warning light 20 is connected to the electronic control unit 10so that it is driven to be illuminated to generate a warning indicativeof the occurrence of abnormality when the abnormality determinationelement 123 in the microcomputer 12 determines the presence ofabnormality in the injectors 5 (fuel system).

[0047] Now, a concrete processing operation of the control unit 10according to the first embodiment of the present invention asillustrated in FIG. 1 will be described while referring to flow chartsof FIG. 2 and FIG. 3.

[0048]FIG. 2 shows a processing routine for carrying out the forced fuelcorrection control, which is performed by the forced fuel correctionelement 122 in the microcomputer 12 until abnormality determination hasbeen finished after starting of the engine 1.

[0049]FIG. 3 shows a processing routine for determining partialabnormality in the injectors 5 (fuel system), which is executed by theabnormality determination element 123 in the microcomputer 12 during theforced fuel correction control.

[0050] Here, it is assumed that the abnormality determination element123 determines the abnormal state of an injector 5 for a part of theplurality of cylinders as partial abnormality in the fuel system.

[0051] In FIG. 2, at first, the forced fuel correction element 122determines whether the amount of fuel supplied to the engine 1 is in astate of being controlled in a feedback manner (step S1).

[0052] When it is determined in step S1 that the fuel system is underfeedback control, a determination is then made as to whether the engineoperating condition is in a stable state (step S2).

[0053] When it is determined in step S2 that the engine 1 is in a stablestate (that is, YES), a determination is further made as to whetherabnormality determination of the injectors 5 (fuel system) under theforced fuel correction control has been carried out after starting ofthe engine (step S3).

[0054] When it is determined in step S3 that the abnormalitydetermination have not yet been carried out after the engine starting(that is, NO), the forced fuel correction control for abnormalitydetermination is effected (step S4), and the processing routine of FIG.2 is ended.

[0055] On the other hand, when it is determined in step S1 that the fuelsystem is not under feedback control (that is, NO), ordinary feedbackcontrol is carried out (step S5), and the processing routine of FIG. 2is ended.

[0056] Moreover, when it is determined in step S2 that the operatingcondition of the engine 1 is not in a stable state (that is, NO), orwhen it is determined in step S3 that abnormality determination for theinjectors 5 has already been carried out (that is, YES), the processingroutine proceeds to the ordinary feedback control step S5.

[0057] Thus, when the operating condition of the engine 1 after startingthereof is under the fuel amount feedback control based on the detectionsignal (concentration of oxygen) from the oxygen sensor 9 and in astable state, the forced fuel correction control is carried out onlyonce by the forced fuel correction element 122, and thereafter theforced fuel correction control is continued until the abnormalitydetermination for the fuel system is ended.

[0058] Subsequently, in FIG. 3, the abnormality determination element123 first determines whether the engine 1 is under the forced fuelcorrection control performed by the forced fuel correction element 122(step S11), and when it is determined that the engine 1 is not under theforced fuel correction control (that is, NO), the processing routine ofFIG. 3 is ended at once.

[0059] On the other hand, when it is determined in step S11 that theengine 1 is under the forced fuel correction control (that is, YES), theoutput signal (concentration of oxygen) from the oxygen sensor 9 isprocessed so as to check the state of the oxygen concentration detectedduring the forced fuel correction control (step S12).

[0060] Here, note that the concrete signal processing in step S12 isdescribed in the above-mentioned first prior art example (JapanesePatent Application Laid-Open No. 4-269350) for instance, and hence adetailed description thereof is omitted.

[0061] Thereafter, it is determined whether the fuel system is partiallyabnormal from the signal processing result carried out in step S12 (stepS13), and when it is determined that the fuel system is not partiallyabnormal (that is, NO), the processing routine of FIG. 3 is ended atonce.

[0062] On the other hand, when it is determined in step S13 that thefuel system is partially abnormal (that is, YES), a fuel system partialabnormality determination flag Fl is set to “1” in (step S14), and theprocessing routine of FIG. 3 is ended.

[0063] Hereafter, the abnormality determination element 123 drives thewarning light 20 to warn the occurrence of abnormality, thereby enablinga prompt action to be taken for coping with the abnormal situation.

[0064] Thus, the forced fuel correction control is carried out by theforced fuel correction element 122 so that the concentration of oxygendetected by the oxygen sensor 9 during the forced fuel correctioncontrol is checked to determine whether the fuel system for a part ofthe cylinders is abnormal, as a result of which it is possible to makeabnormality determination in an accurate manner even if there is achange in the engine load or the number of revolutions per minute of theengine 1 in the course of the feedback control operation performed byusing the oxygen sensor 9.

[0065] In addition, abnormality determination is carried out in a stableoperating state of the engine after starting thereof, abnormality in apart of the injectors 5 (fuel system) can be determined in a accuratemanner with higher reliability.

[0066] Embodiment 2.

[0067] Although in the above-mentioned first embodiment, abnormality inthe oxygen sensor 9 has not been taken into consideration, the presenceor absence of abnormality in the oxygen sensor 9 may be determinedbefore abnormality determination for a part of the fuel system has beenmade, and the above-mentioned abnormality determination processing forthe fuel system may then be carried out after confirming that the oxygensensor 9 is in a normal state.

[0068] Hereinafter, reference will be made to a second embodiment of thepresent invention in which a function of determining abnormality in theoxygen sensor 9 is added, while referring to a flow chart of FIG. 4.

[0069] In FIG. 4, the same or like processing steps as those describedabove (see FIG. 3) are identified by the same symbols while omitting adetailed description thereof.

[0070] In this case, after it has been determined that the engine isunder the forced fuel correction control in step S11 and the processingof the output signal of the oxygen sensor 9 has been performed in stepS12, the abnormality determination element 123 determines based on thesignal processing result whether the oxygen sensor 9 is abnormal (i.e.,the presence or absence of abnormality) (step S23).

[0071] Here, note that the concrete signal processing in steps S12 andS13 are described in the aforementioned second prior art example(Japanese Patent Application Laid-Open No. 2-11840) for instance, andhence a detailed description thereof is omitted.

[0072] When it is determined in step S23 that the oxygen sensor 9 isabnormal (that is, YES), an abnormality determination flag F2 of theoxygen sensor 9 is set to “1”, and the processing routine of FIG. 4 isended.

[0073] Accordingly, the fuel system partial abnormality determinationprocessing (steps S13 and S14) is never performed when the oxygen sensor9 is abnormal, and hence abnormality determination for the fuel systemwith low reliability at the time of abnormality in the oxygen sensor 9is avoided.

[0074] On the other hand, when it is determined in step S23 that theoxygen sensor 9 is not abnormal but normal (that is, NO), the fuelsystem partial abnormality determination processing (steps S13 and S14)is carried out, and the processing routine of FIG. 4 is ended.

[0075] Hereafter, the abnormality determination element 123 drives thewarning light 20 to warn the occurrence of abnormality in the oxygensensor 9, thereby enabling a prompt action to be taken for coping withthe abnormal situation.

[0076] At this time, for warning information about the abnormal state ofthe oxygen sensor 9, the warning light 20 may be driven in a form (forinstance, the blinking cycle of the warning light 20 may be changed, ora separate lamp of a different color may be driven, etc.) different fromthe aforementioned case of warning abnormality in the fuel system.

[0077] Thus, before determining the presence or absence of abnormalityin the injectors 5, the abnormality determination element 123 determinesthe presence or absence of abnormality in the oxygen sensor 9 based onthe concentration of oxygen detected by the oxygen sensor 9 in thecourse of the forced fuel correction control performed by the forcedfuel correction element 122, so that only when the oxygen sensor 9 isnot abnormal (i.e., normal), a determination is made whether any of theinjectors 5 is abnormal, thereby making it possible to further improvereliability in the fuel system partial abnormality determination.

[0078] In addition, the abnormality determination can be carried out ina reliable manner at higher frequencies by determining abnormality inthe fuel system for a part of the cylinders simultaneously with theabnormality determination of the oxygen sensor 9.

[0079] Embodiment 3.

[0080] Although in the above-mentioned first embodiment, onlyabnormality in part of the injectors 5 (fuel system) has been determinedunder the fuel amount feedback control, abnormality determination in thefuel system may be made by taking a logical sum with the abnormalitydetermination result of the fuel system based on the amount of feedbackcontrol (i.e., the amount of control fuel under feedback control).

[0081] Hereinbelow, reference will be made to a third embodiment of thepresent invention in which a fuel system abnormality determiningfunction based on the amount of feedback control is added, whilereferring to a flow chart of FIG. 5.

[0082] In this case, when the amount of fuel controlled by the feedbackcontrol element 121 varies from a reference value by a prescribed valueor more, the abnormality determination element 123 determines that theamount of control fuel is abnormal, and sets the fuel system abnormalitydetermination flag Fb to “1”.

[0083] Here, note that the fuel system abnormality determinationprocessing based on the amount of feedback control is described in theaforementioned third prior art example (Japanese Patent ApplicationLaid-Open No. 63-219848) for instance, and hence a detailed descriptionthereof is omitted.

[0084] In FIG. 5, the abnormality determination element 123 firstdetermines whether the fuel system abnormality determination flag Fbbased on the amount of feedback control is set to “1” (step S31).

[0085] When it is determined in step S31 that the fuel systemabnormality determination flag Fb is equal to “0” (Fb=0) (that is, NO),it is then determined whether the fuel system partial abnormalitydetermination flag Fl is set to “1” according to the above-mentionedstep S14 (see FIG. 3 and FIG. 4) (step S32).

[0086] When it is determined in step S32 that the fuel system partialabnormality determination flag Fl is equal to “0” (Fl=0) (that is, NO),the fuel system is normal and hence a final fuel system abnormalitydetermination flag FF is cleared to “0” (step S33), and the processingroutine of FIG. 5 is ended.

[0087] On the other hand, when it is determined that the fuel systemabnormality determination flag Fb is equal to “1” (Fb=1) in step S31(that is, YES), the fuel system is regarded as abnormal, and the fuelsystem abnormality determination flag FF is set to “1” (step S34), andthe processing routine of FIG. 5 is ended.

[0088] Additionally, when it is determined that the fuel system partialabnormality determination flag Fl is equal to “1” (Fl=1) in step S32(that is, YES), the fuel system is similarly regarded as abnormal, andthe processing routine proceeds to step S34.

[0089] Thus, when the amount of fuel controlled by the feedback controlelement 121 varies from the reference value by a prescribed value ormore, the abnormality determination element 123 determines that theamount of control fuel is abnormal and sets the fuel system abnormalitydetermination flag Fb to “1”, whereas when it is determined that atleast one of the injectors 5 and the amount of control fuel is abnormal,the abnormality determination element 123 determines that the fuelsystem including the injectors 5 is abnormal, and sets the fuel systemabnormality determination flag FF to “1”.

[0090] That is, the abnormality determination element 123 determinesthat the fuel system is abnormal, depending upon either one (logicalsum) of the result of the fuel system abnormality determinationaccording to the amount of feedback control and the result of the fuelsystem partial abnormality determination.

[0091] As a result, the abnormality determination can be carried out athigher frequencies or highly frequently.

[0092] Although in the foregoing embodiments, a plurality of injectors 5have been employed, the present invention can of course be applied tothe case in which a single injector is used for supplying fuel to aplurality of cylinders.

[0093] While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modifications or changes within the spirit andscope of the appended claims.

What is claimed is:
 1. An abnormality diagnosis apparatus of an internalcombustion engine comprising: an oxygen sensor for detecting aconcentration of oxygen in exhaust gases of an internal combustionengine; an injector for injecting fuel into said internal combustionengine; a feedback control element for driving said injector accordingto said concentration of oxygen to control an amount of fuel supplied tosaid internal combustion engine in a feedback manner; a forced fuelcorrection element for correcting an amount of fuel controlled by saidfeedback control element in a forced manner; and an abnormalitydetermination element for determining the presence or absence ofabnormality in said injector; wherein said abnormality determinationelement determines the presence or absence of abnormality in saidinjector based on said concentration of oxygen detected by said oxygensensor in the course of a forced fuel correction control operationcarried out by said forced fuel correction element.
 2. The abnormalitydiagnosis apparatus of an internal combustion engine according to claim1, wherein said forced fuel correction element carries out the forcedfuel correction control on said amount of control fuel when theoperating condition of said internal combustion engine is in a stablestate.
 3. The abnormality diagnosis apparatus of an internal combustionengine according to claim 1, wherein before determining the presence orabsence of abnormality in said injector, said abnormality determinationelement determines the presence or absence of abnormality in said oxygensensor based on said concentration of oxygen detected by said oxygensensor in the course of the forced fuel correction control operationcarried out by said forced fuel correction element, and furtherdetermines the presence or absence of abnormality in said injector onlywhen said oxygen sensor is not abnormal.
 4. The abnormality diagnosisapparatus of an internal combustion engine according to claim 3, whereinsaid abnormality determination element is provided with warninginformation element and drives said warning information element when itis determined that said oxygen sensor or said injector is abnormal. 5.The abnormality diagnosis apparatus of an internal combustion engineaccording to claim 1, wherein when the amount of fuel controlled by saidfeedback control element varies from a reference value by a prescribedvalue or more, said abnormality determination element determines thatsaid amount of control fuel is abnormal, and further determines thatsaid fuel system including said injector is abnormal when it isdetermined that at least one of said injector and said amount of controlfuel is abnormal.